Thursday, January 27, 2011

A blunderbuss is a short range defensive weapon that reached its popularity in the 18th and 19th centuries. We will study this unique class of firearms in this post.

A typical blunderbuss is a muzzle-loader with a relatively short barrel that has a distinctive trumpet-shaped flare at the muzzle end of the barrel. The caliber of this weapon is typically large and it was often used by filling the barrel with multiple smaller pellets.

A Blunderbuss. Note the typical flared muzzle end of the firearm.

The original term for this weapon was donderbuss and this name appears to be Dutch. The word "donder" means "thunder" and "buss" means "pipe" in Dutch and German languages. Blunderbuss class weapons also appeared in handgun form, intended for cavalry. These early pistol blunderbusses often had decorations around the muzzle that looked like a dragon with an open mouth and hence were called "dragons". The cavalrymen who used such blunderbuss pistols were therefore called "dragoons". One such example of a dragon pistol is shown below:

The trumpet shape at the muzzle is the distinctive blunderbuss feature that distinguishes it from other firearms of that period. Since a blunderbuss is designed to fire several pellets at the same time, the flare was thought to increase the spread of pellets. The flare also makes it easier to load powder and pellets into the firearm. People mounted on horseback, or in a rocking coach or ship, found this feature very useful indeed. Also, since these are shorter weapons compared to the muskets of the era, they are more easy to manipulate on horseback or a ship deck. This is why they were very popular among cavalry, pirates, mail coach guards, naval personnel etc.

Blunderbusses designed for navies and pirates typically had their barrels made of brass instead of iron, to prevent rusting. Since they are designed to spread multiple pellets around, one such shot could easily deal with several closely packed enemies with a single shot. Hence, they were often carried into action by boarding personnel.

While most blunderbusses were designed as everyday practical weapons, some blunderbusses were also works of art:

The above weapon was custom made for Tipu Sultan, who ruled the Kingdom of Mysore in the 18th century. This fine weapon uses a flintlock firing mechanism and the barrel has engravings and gold inlays. Tipu Sultan was known to employ several European craftsmen and this weapon represents the latest in technology of that period.

As breech-loading weapons became more common in the 19th century, the blunderbuss gradually became obsolete and was replaced by the carbine.

Monday, January 24, 2011

In most rifle configurations, the trigger is located right underneath or very close to the the firing action. This means that the barrel starts right about where the trigger is. This has generally been the standard configuration for most firearms ever since firearms were invented. However, in the beginning of the 1900s, the concept of having a trigger ahead of the action was invented. This type of action is called a bullpup design and we will study about this type of design in this post.

Since the bullpup design has the trigger in front of the action, this means that the action sits close to the back of the buttstock and closer to the user's face. That means the overall length of the weapon is reduced. Also, since the stock contains part of the barrel and the action, the stock is much smaller and hence, a bit lighter than a conventional rifle. For example, the Steyr AUG rifle that you see in the image above has a 20 inch long barrel and uses 5.56 mm. NATO caliber cartridges, but is only 790 mm. long and about 3.6 kg in weight. By comparison, a conventional configured rifle, such as an M16A2, also has a 20 inch long barrel and uses 5.56 mm. NATO caliber, but is 1010 mm. long and 4 kg. in weight, which means that we save about 25% in length and about 10% in weight with a bullpup configuration.

The original bullpup design was invented in England in 1901. The Thorneycroft carbine was chambered for a .303 rifle cartridge and held five rounds in an internal magazine. It was 7.5 inches shorter and 10% lighter than the standard Lee Enfield rifle, which was the standard infantry arm of the British military and also fired a .303 cartridge. The Thorneycroft rifle suffered from recoil and ergonomics and was not adopted for military service. Later inventors tried to improve the design, such as a couple of French inventors in the 1920s and 1930s, but were not widely accepted. The Enfield factory came out with the EM-2 after World War II, but since it was not designed for NATO caliber, it faded from use very soon after. However, the British did not forget the concept of a bullpup configuration and later designed the L85 assault rifle in 1985, which is the current standard British military firearm.

Public domain image of a British L85A1 assault rifle

However, it wasn't the British that came out with the first successful bullpup configured rifle. That honor goes to the Steyr AUG which came out in 1977. The Steyr AUG was adopted by Austria initially and was later adopted by over 25 countries. Unlike previous attempts, the Steyr AUG was highly reliable, light and accurate and showed off the advantages of a bullpup configuration. France followed soon after with their new standard infantry rifle, the FAMAS, in 1978. This was followed by the UK's L85A1 and L85A2 models in the 1980s and early 1990s. Soon, many other countries followed suit, such as the Chinese QBZ 95, Singapore's SAR-21 and the Israeli Tavor TAR-21.

While bullpup designs are shorter and lighter (and therefore easier to maneuver in confined spaces), there are a few disadvantages as well. One of the early ones is that the ejection port of the rifle sits a lot closer to the user's face. Since most rifles eject spent cartridges to the right, left handed shooters have to shoot right-handed style to avoid getting a hot cartridge to the face. Some assault rifles (such as the Steyr AUG and FAMAS) get around this issue by allowing the user to easily swap the bolt and ejection cover around, so that left handed users can make the rifle eject to the left. Other rifles solve this by ejecting the spent cases forwards or downwards. Other issues with bullpup configurations are that the noise appears louder as the firing chamber is closer to the user's ears and magazine changes take a little longer, due to the ergonomics of this configuration. On the other hand, with the success of the Steyr AUG, many other militaries have also adopted rifles with bullpup configurations, because of the lighter and shorter nature of such designs.

Sunday, January 23, 2011

In the last post, we studied some of the criteria that militaries follow when selecting a new firearm for their inventory. Among the extensive list of selection criteria is a set of torture tests, which test the firearm for reliability, functionality and ease of use under demanding conditions. While military tests are pretty demanding, they are not necessarily the toughest tests that a firearm may be subject to.

A few years ago, one enterprising gentleman decided to conduct a series of tests to determine exactly how reliable his Glock model 21 pistol was. He fully documented his process and even took video footage to prove that he'd actually conducted the tests.

The entire series test is documented here. The first couple of pictures in his original post seem to have disappeared, but a backup copy of that legendary post was also archived here, with the first few pictures intact. Note that the second link only has pictures, but not the links to the movies, which the first link contains. It is a very interesting read. The tests he conducted seem to be even more demanding than military tests. Bear in mind that this particular pistol was almost 10 years old already and had been well used and abused, before he even started conducting the tests. Also, half-way through the torture test process, he took the very same weapon to a weekend gun match!

While this is an extreme case of mistreatment, it is interesting to note that his weapon still managed to function after all that had been done to it. Note that the gentleman conducting the tests is a professional expert and such tests should NEVER be conducted by readers of this blog.

Friday, January 21, 2011

In the history of firearms, the most stringent requirements are usually applied when a weapon is selected for military use. This is because military weapons:

Should be able to work in demanding conditions (snow, heat, rain, dirt etc.)

Should be reliable, extremely resistant to damage and have long service life.

Should have good range and stopping power.

Should be simple to service in the field.

Should not be too expensive, because a large number of them will be ordered.

Should perhaps maintain compatibility with some other existing system (e.g. use cartridges of a specific caliber, be under a certain size to fit into vehicles, have at least a certain magazine capacity etc.)

The weapon that is selected by a military strikes a balance between these various factors. In this posting, we will look at some historical selection criteria for handguns from various regions around the world.

The first set of criteria we will look at is the requirements of the US Army in 1906 for a new handgun. A few years earlier, US Army units in the Philippines had discovered that the standard Army revolver at that time, a revolver chambered in .38 Long Colt cartridge, was not sufficient to stop a charging Moro tribesman high on narcotics. With that in mind, the US Army Ordinance Department (headed by Colonel John Thompson, who later invented the Tommy gun), did some experiments and determined that a .45 caliber cartridge had the stopping power needed. Therefore, one of the first requirements of the new handgun was that it should be able to shoot the new .45 caliber cartridge. The US Army also subject all submitted handguns to the following torture tests:

Each gun was to fire 6,000 rounds.

Each gun would shoot 100 rounds at a time and then allowed to cool for 5 minutes before shooting again.

Every 1,000 rounds fired, the gun was to be oiled and cleaned before firing again.

After firing 6,000 rounds was completed, the gun was to be tested with deformed cartridges (i.e.) some that seated too deeply, some that were not seated enough etc.

The gun would be exposed to acid to test rust resistance, buried in sand and mud to test reliability etc.

Designs were submitted by Colt, Luger, Knoble, Bergmann, White-Merrill, Smith & Wesson and Savage. The Colt entry was designed by the renowned designer John Browning. The Browning design easily passed all the tests and became known as the M1911 pistol (as it was accepted officially in 1911). In the words of the selection committee:

"...the board was of the opinion that the Colt is superior, because it is more reliable, more enduring, more easily disassembled when there are broken parts to be replaced, and more accurate."

Now we will look at some of the requirements for the Austrian military in 1980, when selecting a new firearm. The Austrians were looking for a handgun to replace their old World War II era Walther P38s. Among the criteria specified:

The design has to be self-loading (i.e.) it should load a new cartridge automatically after an old one is fired.

The weapon must fire the NATO standard 9x19 mm. parabellum round (same as the old Walther P38)

Magazine of the weapon should not require any means of assistance for loading.

Minimum capacity of the magazine should be 8 rounds.

All actions necessary to prepare the pistol for firing and any actions required after firing must be done single-handed, either right or left-handed.

Pistol must be secure from shock. Tests to be conducted by dropping the pistol from a height of 2 meters onto a steel plate from various angles.

Pistol should allow for disassembly and reassembly of the main parts, without using any tools.

Maintenance and cleaning of the pistol should be done without tools.

Pistol should not have more than 58 parts (which was the number of parts on the Walther P-38)

Gauges, measuring and precise testing devices must not be necessary for long term maintenance.

All components must be interchangeable with other pistols

No more than 20 malfunctions are permitted during the first 10,000 rounds fired.

After 15,000 rounds, each pistol will be inspected for wear and tear. The pistol will then fire an over-pressured test cartridge generating 5,000 bar (72,518 psi) which is almost 2x the pressure generated by the standard NATO 9x19 mm. parabellum cartridge (which only generates 2,520 bar (36,500 psi)). The critical components must still continue to function properly after firing this over-pressured cartridge.

When handled properly, under no circumstance should the user be endangered by case ejection.

The muzzle energy of the bullet should be at least 441.5 Joules when firing a 9mm. S-Round/P-08 Hirtenberger AG cartridge.

While there were submissions by many well known firearm manufacturers, it was the design by a then unknown firm called Glock that won this contest. Interestingly, since Glock had no previous firearm design experience, the Austrian authorities decided to subject it to the 10,000 round test with no more than 20 malfunctions. To everyone's surprise, the Glock design only suffered one malfunction in 10,000 rounds. None of the other manufacturers' submissions were subject to this grueling test because it was simply assumed that the others would pass as well!

Other torture tests included testing under extreme heat, ice, sand and mud and testing the firearms both after oiling and in an unlubricated state etc. They also considered other factors such as the time taken to train new shooters, number of parts to manipulate to make the weapon ready to shoot and ease of maintenance. Glock's design not only passed these tests with flying colors, they were far ahead of any other competing pistol, while also being 25% cheaper than the next lowest bidder. Glocks have since been accepted by many other militaries and police forces around the world.

Monday, January 17, 2011

People who use shotguns for hunting birds often use ammunition that contain multiple pellets or ball bearings. When such a cartridge is shot, the pellets spread out about a certain area, depending on the distance to the target. The pellets leave the shotgun in approximately the same order that they were in the cartridge and continue in a compact mass, until they hit a target, or fall on the ground. In order to reduce the area of concentration of the pellets, people employ various devices on the barrel such as a cylinder choke, skeet choke, modified choke, full choke etc. Of course, different choke types work differently with different ammunition types and hence testing is needed to determine the most effective combinations.

The standard way to test the shotgun pattern is to take a square sheet of paper around 40-45 inches long on each side. The tester mounts this sheet of paper at a distance of 40 yards. The tester then loads the shotgun with a cartridge that has a known number of pellets and shoots at the target. After this, the shooter looks at the paper and draws a circle of 30 inches diameter around the area with the greatest concentration of pellets.

Then the tester counts the number of holes inside this 30 inch circle. Say there are 150 holes inside the circle and the tester knows that the cartridge had 200 pellets loaded. Therefore the tester can say that this shotgun shoots with a 75% pattern for this choke and cartridge load combination.

The tester repeats this test five or more times with a given cartridge load and computes the average to get the shotgun pattern. Obviously, the type of choke used, the number and size of the pellets in the cartridge and the material of the pellets all may have an effect on the pattern density, so the tester tries the same test out with different combinations to find out which of these produce the best patterns.

In order to keep the tests accurate, one needs to make sure that the cartridges used in this test have the same number of pellets or ball bearings each time. One way to do this is to weigh the pellets before loading them into the cartridge. The following table illustrates the average number of pellets per ounce of different standard pellet sizes for both lead and steel pellets:

Of course, this assumes that the pellets are all of the same shot size. Some people don't believe in weighing the pellets to get a count. Instead, what they do is use a simple counting device, such as the one shown below:

Public domain image. Click on image to enlarge.

It consists of a flat trowel made of brass or steel, with a number of holes drilled into it. There is a sliding cover on the handle that can be used to vary the number of holes exposed on the face of the trowel. The tester pushes the trowel into a pile of pellets or bearings and slowly withdraws it. Pellets will stick to the holes and those that are not in any holes can easily be separated. Any misshapen or undersized pellets are also easily visible, so they can be removed as well. The tester can thus easily load the exact same number of pellets into multiple cartridges.

Sunday, January 16, 2011

When testing firearms and ammunition for accuracy and range, it is necessary to minimize human error as much as possible. When a human being shoots at a target, it is human nature that there is a lack of consistency between shots. A person may hold the firearm tighter or looser, shake the firearm more or less, vary the trigger pull force and react to the recoil differently from shot to shot. In order to eliminate variability for these factors, the industry developed machine rests (a.k.a bench rests). We will study these in this post.

A machine rest should ideally have the characteristic that it simulates a human shoulder or arm, so that it absorbs the recoil from a firearm as though a human were holding it. This is very important because if the machine rest is completely fixed, it will result in damage to the firearm's stock, bedding or recoil lugs. The machine rest should also be able to return back to zero (i.e.) back to its previous position before firing it. There should be some provision to pull the trigger by mechanical means, so that the trigger pull force and speed are consistent between shots. Some machine rests also have gauges to record the recoil force generated by the firearms as well.

In the above image, we have a machine rest designed in the 1890s, which was used by Field magazine to evaluate various firearms. It was made of iron, so that it was relatively portable. Points of interest are the spring balance H and toggle joint I. The spring balance records the recoil force and the toggle joint ensures that the varying strength of the spring at different positions is equalized out to provide a constant resistance. The device J, which is located under the stock of the rifle is an oil reservoir which has a cylinder and piston. This returns the firearm slowly back to its initial firing position, after it has been discharged.

Here's what a typical modern machine rest for rifles looks like:

This particular modern rifle rest is made by Hyskore and has interchangeable shock absorbers (compression dampers) for different rifle types. In this particular model, the shock absorbers are filled with nitrogen gas. It also has various knobs to adjust elevation and windage precisely and aim the rifle to the target. In addition, it has a remote controlled hydraulic trigger pull, so that there is consistency between one trigger pull and the next.

Next, we will look at another well known brand of machine rests used for handguns:

The above is a Ransom International made rest, which is pretty much the gold-standard when it comes to accuracy testing of handguns. Ransom International introduced the Master Series Rest into the market in 1969 and the Master Series models are still being sold today. In fact, most major handgun manufacturers use this model for accuracy testing. Like the other rests, this also simulates the grip and recoil absorption of a human hand very closely and it also has the facility to return the firearm back to its initial position after the shot. The trigger is activated by a little lever on the side, to provide consistent trigger pulls each time.

While major manufacturers use machine rests to ensure quality control of their products, these are also used by owners to evaluate their firearms and ammunition brands. For example, ammunition from different manufacturers come in different qualities. A tester can shoot X rounds each from different brands and determine which ammunition manufacturer produces cartridges that shoot uniformly best. Also, many new semi-automatic pistols have a tendency to shoot the first cartridge in the magazine in a different place than the other ones. Using a machine rest allows a tester to evaluate if a particular pistol has this characteristic. Some revolvers sometimes have some chambers in the cylinder that shoot at a different point than the rest of the chambers. Using a machine rest allows the tester to mark out which chamber(s) shoot differently and perhaps not load those chambers.

One of the tests of cartridges is the penetration test. This test shows how effectively a particular type of bullet will penetrate its target. As we studied earlier, there are different types of bullets: hollow point, full-metal jacket, soft-point etc. There are also different types of targets: For example, a bullet shot at vermin such as rats, needs to expand really quickly after it hits the target, to have any effect on the animal. It should not exit out the other end without expanding first. However, the same bullet will not be as effective on a larger animal, if it expands too early, as it will not hit a vital organ and not ensure a quick kill.

Penetration testing in earlier years used to involve using thick brown paper sheets or strawboards. These were stacked together horizontally and shot at, and the count of the number of sheets or boards penetrated were tallied up and compared to each other. The following image shows one of these test racks

Public domain image. Click image to enlarge.

In modern times, the medium of choice is a material called ballistic gelatin. The reason for using ballistic gelatin is because it has about the same density of human or animal tissues. Ballistic gelatin is also preferable to actual muscle tissues, since its properties can be more carefully controlled to produce a consistent medium for doing multiple comparative tests. It must be noted that ballistic gel doesn't completely simulate actual body structure, since it doesn't have any skin or bones, which are much tougher and harder than flesh tissue.

The standard formula used for testing is called "10% ballistic gel". It consists of mixing 1 part by mass of powdered ballistic gel formula with 9 parts of water at a temperature of 54.5 C (130 F). The mixture is poured into standard molds (per the INS National Firearms Unit test, the standard mold size is 6" x 6" x 16" for handguns. Other standards bureaus may have different standard test sizes) and the mixture is chilled to 4 C (39 F) and allowed to set.

Before conducting the actual tests, the gel block is initially calibrated by firing a standard 4.5 mm. steel ball bearing from an air gun, over a chronograph and into the gel block. The air gun should shoot the ball bearing at a velocity of 183 ± 3 meters/sec. (600 ± 10 feet/sec.), which can be verified by the chronograph. If the gel block was prepared correctly, the penetration of the ball bearing should be between 8.3 to 9.5 cm. (3.25 - 3.75 inches). If this is the case, then the gel block may be used for standardized testing.

Friday, January 14, 2011

In our last post, we studied a few methods that measure the time taken by the bullet to travel a known distance and thereby calculate its velocity. These methods fall under the class of chronograph methods. All these methods were generally inferior to the ballistic pendulum method for a variety of reasons, chiefly the inability to measure small amounts of time accurately and also the inability to ensure that the targets were moving at uniform rates.

While the ballistic pendulum method was superior for a long time, one of the issues it had was the weight of the apparatus. For testing the velocity of ordinary rifles or shotguns, the ballistic pendulum alone needs to weigh around 25 kg. (55 lbs.), without considering the weight of the supporting frame. When people try to scale this method for larger cannon balls, the weight of the pendulum apparatus increases exponentially. For example, in 1781, one Mr. Hutton tried to measure the velocity of cannon balls weighing just 3 pounds and his pendulum weighed about 315 kg. (approx. 700 lbs.). During the period of 1842 to 1847, one Major Alfred Mordecai from the United States Army tried to determine the muzzle velocity of larger guns and built a ballistic pendulum weighing over 4215 kg. (approx. 9300 pounds) and was mounted between two large brick towers. This could only measure velocities for 32 pounders at most. It was estimated that to build a ballistic pendulum to measure velocities for even larger weapons, one would need to build a massive pendulum suspended by the two Brooklyn bridge sized towers!

Meanwhile, the discovery of electricity made chronograph methods much more accurate. It was now possible to measure the beginning and end of a period of time using some sort of electrically operated mechanism. It also became possible to measure very small intervals of time accurately, making chronograph methods much more accurate than was achievable previously.

One of the early chronoscopes was invented by Charles Wheatstone, a noted scientist of the Victorian era. Among his other inventions were a stereoscope, an encryption system, several developments in telegraphy and the wheatstone bridge. His chronoscope consisted of a wooden ring fixed to the muzzle of a gun, with a thin wire running through the middle of it. The target was placed at a known distance and consisted of two plates which were arranged so that the least impact would result in a permanent contact between the two plates. The wires were hooked to an electromagnet mechanism and a small battery. Initially, a continuous circuit would be maintained. Then when the firearm would be discharged, the bullet would leave the muzzle and pass through the wooden ring and cut the thin wire running through the center. This would deactivate the electromagnet, which would then start a special clock driven by a falling weight. When the bullet would hit the target, the second circuit would be completed, which would re-energize the electromagnet and stop the clock. This mechanism was capable of measuring time with a resolution accurate to approx. 1/7300 of a second, which allowed it to calculate bullet velocities very accurately.

A more modernized version used a tuning fork to measure small increments of time. The tuning fork would have a thin stylus attached to one of the arms and a roll of paper would be gradually moved over the stylus. The tuning fork would be activated and deactivated by electricity and the tester would count the number of vibrations of the tuning fork, inscribed on the paper roll, to determine the elapsed time.

Using electricity to measure time became much more popular because the same setup could be used on just about any caliber firearm.

These days, modern chronographs use optical detection or to determine the passage of a bullet through a known distance. For instance, photo-transistors (such as those that work with infrared frequencies) could be used to start and stop a highly accurate stopwatch. The passing bullet shadow causes the circuit to be activated and deactivated at the two ends of a known distance and very high time resolutions can be obtained. Such devices are pretty cheap as well and available for around $100-$200 or so.

In the above images, we have a modern chronograph that can measure bullet velocities between 30 - 7000 feet/sec with 99.5% accuracy. The V arms indicate the area through which the bullet should be shot for the sensors to detect it. The two white strips on the top are light diffusers, so that this device can be used even in bright sunlight. They also help to provide a uniform background so the photo-transistor sensors can easily detect the contrast a passing bullet. In less than bright daylight conditions, the two diffusers can be optionally removed. The digital display automatically calculates the bullet velocity, so all the user needs to do is position this device on a flat surface, such as a table, turn it on and then shoot through the two V areas. High velocity rifles should be shot from at least 3 meters (10 feet) away and lower velocity weapons may be shot from around half that distance to get accurate readings.

Modern chronographs such as the one above make it a breeze to calculate bullet velocities. Due to their lightness and low cost, these are overwhelmingly the method of choice to measure bullet velocities these days.

Tuesday, January 11, 2011

In our previous post, we studied the first accurate method of identifying bullet velocities: the ballistic pendulum method. While the ballistic pendulum method was accurate and remained in use for many decades, it wasn't initially adopted all over Europe perhaps because the inventor was English. Instead there were some other methods developed in some other countries of Europe, all of which were developed after the ballistic pendulum method. Some of these were not as accurate, but were still preferred over the ballistic pendulum method, perhaps because of nationalistic reasons. The interesting thing about these methods is that while they were more inaccurate than the ballistic pendulum method at the time they were invented, they laid the foundations for more modern and accurate methods of determining bullet velocities.

In 1767, an Italian named Mattei came up with a method to measure bullet velocities. His method consisted of a vertical paper cylinder which was mounted on a wooden frame. The frame was made to rotate by using a cord and a weight. Once a uniform known speed was attained by it, the bullet was fired through it, perpendicular to the axis of the cylinder. The bullet passed through the paper cylinder and left two holes on the surface. The two holes gave the arc through which the cylinder had rotated as the bullet passed through it. By computing the length of the arc and knowing the diameter and the rotational speed of the cylinder, one could compute the bullet velocity. However, this method's precision was dependent on three factors: (a) the diameter of the cylinder, (b) knowing the rotational speed accurately and (c) the uniformity of the rotation. This machine was also not very effective against faster moving bullets, because it could not measure times less than 1/30th of a second, during which time a modern bullet, such as that fired by an M-16 rifle, could easily cover 100 feet (30 meters), which means you'd have to use a cylinder at least 100 feet in diameter to measure the speed of an M-16 bullet reasonably. It was also very hard to make sure the cylinder was rotating uniformly and so the device was not very accurate either.

In 1804, a French officer named Colonel Grobert invented another method to determine bullet velocity based on similar principles as Mattei's method. In Grobert's method, two large disks about 6.5 feet in diameter, made of cardboard, were attached to the same horizontal axle. In Grobert's original design, the two disks were placed 13 feet apart. The axle was rapidly rotated by means of an endless chain in combination with a flywheel and a windlass. When the rotation of the axle was judged to be at a constant speed, the tester then aimed at the disks and fired a shot through them. The bullet pierced through both disks, but since they were rotating rapidly, the exit hole through the second disk was not in the same line as the exit hole through the first disk. By looking at the positions of the two holes, one could determine the angle of revolution. Since the distance between the two disks was known and the speed of rotation was also known, the tester could calculate the bullet velocity. However, this method had the same weaknesses as the Mattei method described above.

The next step to correct these above problems was invented by another French officer, one Colonel Dabooz, in 1818. His method involved a gravity apparatus to measure bullet velocities.

His apparatus consisted of two screens, two pulleys, a cord and a counterweight. In his method, a fixed screen was placed precisely 50 yards from the muzzle of the firearm to be tested. Directly in front of the fixed screen was another screen, which was suspended by the cord. The cord passed through two pulleys and the other end was right in front of the muzzle of the gun and was tied to a counterweight, which held the movable screen in place. The firearm was aimed at the screens. When the firearm was discharged, the bullet would cut the cord as it left the barrel. This would release the movable screen, which would start falling. The bullet would travel 50 yards and pass through both screens. Since the movable screen was falling during this time, the hole in the movable screen would not be at the same height as the hole in the fixed screen. Knowing the acceleration due to gravity and measuring the distance between the holes in the two screens, the tester could calculate how much time the bullet took to travel 50 yards and from this, he could calculate the bullet velocity. This method had the advantage that a constant acceleration was imposed on the falling screen (since acceleration due to gravity remains constant), which made the time measurement more reliable. To measure the velocities of faster moving bullets, the distance between the two pulleys could be increased and reasonably accurate measurements could be made. The one error in this method is that it assumed that the movable screen would begin to fall as soon as the bullet passed through the cord.

The reader might note that while these three method use different ideas, they have one thing in common: they all measure the time taken for a bullet to travel through a known distance and from this, they determine the bullet velocity. This is unlike the ballistic pendulum method, which uses the principle of conservation of momentum to determine the bullet velocity. While these methods were not as accurate as the ballistic pendulum method when they were invented, they laid the foundation for the concept of cronographs. With the invention of electricity, the cronograph concept became more practical and more accurate and it eventually replaced the ballistic pendulum method. We will study practical cronographs in the next post.

Monday, January 10, 2011

In our previous posts, we've seen how to measure chamber pressures and trigger pull force. In this post, we will study how to measure bullet velocity. This will be a study in two posts since there is much to discuss on this topic.

First, why does someone need to know the bullet velocity. For one, it is useful to compute the kinetic energy carried by the bullet. We can obtain the bullet mass by weighing it and if we can obtain its velocity, then its kinetic energy is computed by simple mathematics: kinetic energy is calculated as (1/2 * m * v 2), where m = mass of bullet and v = velocity of the bullet. Also, it is useful to know how much velocity a bullet loses over distance to determine effectiveness over various distances.

The first really good method to determine the bullet velocity appeared in a book published in 1742 called New Principles of Gunnery written by Benjamin Robins, an English mathematician with an interest in ballistics. This was a very influential book, as it introduced military men to the teachings of Newtonian physics. This book also contributed to the development of artillery towards the end of the 18th century and was responsible for introducing calculus to the syllabus of many military academies. In fact, Benjamin Robins is considered one of the founders of modern aerodynamics and the father of modern gunnery. Before this book appeared, gunnery was simply a matter of guesswork. After this book was published, it became an exact science. The work was so influential that the famous Swiss mathematician and physicist, Leonhard Euler, himself translated this book into German.

In this book, Robins introduced the concept of a ballistic pendulum. In his original book, this is a heavy iron weight with a wooden board covering its face. The bullet is fired into the pendulum weight and gets embedded into the wooden board. The act of the bullet hitting the pendulum transmits the bullet's momentum into the pendulum, causing it to swing, as shown in the image below:

Public domain image

The pendulum also has a ribbon attached to the arm and gripped loosely by a clamp. As the pendulum swings, it pulls a length of ribbon out with it. By measuring how much of the ribbon was pulled out, we can determine the length of the pendulum's arc. We can also measure how many times the pendulum swings in one minute (i.e. its oscillation period).

An image of the original apparatus as published in Benjamin Robins' book, New Principles of Gunnery

Click on image to enlarge.

Robins' original formula used the oscillation period and mass of the pendulum and the pendulum arm to calculate its rotational moment of inertia and from there, the bullet's velocity. In his original work, he ignored the effect of the bullet not hitting the center of mass of the pendulum weight. The very next year, an updated formula to correct for this omission appeared in a paper published by the Royal Society of England. Meanwhile, Leonhard Euler, who was unaware about the corrected formula, independently determined the same corrected calculation and published the corrected version when he translated Robins' book into German. The formula is computed as:

v = 614.58 * g * c * (p + b) / (b * i * r * n)

where:

v = Velocity of bullet in meters/sec

g = Distance from the pivot to center of gravity of the pendulum in meters

c = The chord (i.e.) length of swing of the pendulum determined by the ribbon in meters

p = Mass of the pendulum in kg.

b = Mass of the bullet in kg.

i = Impact point (i.e.) distance from the pivot to the point of impact of the bullet in meters

r = Radius (i.e) distance of the pivot to the point of attachment of the ribbon in meters

n = Number of oscillations made by the pendulum in one minute

The same formula can be switched to get velocity in feet/sec and if one uses feet instead of meters and pounds instead of kg.

If one were to ignore the effects of rotational inertia (whose effect is somewhat small to begin with) and ignore the mass of the pendulum arm (modern day materials technology can make the pendulum arm very lightweight compared to the weight of the pendulum), this formula can be simplified even further as:

v = ( 1 + p / b) * sqrt(2 * G * h)

where G = acceleration due to gravity and h = height of the pendulum's travel and the other terms are the same as the previous formula. If the simplified formula is used, one doesn't even need to calculate the pendulum's period of oscillation and it is sufficient to only weigh the bullet and the pendulum and measure the height of the pendulum's travel. Of course, this simplified formula doesn't provide as accurate an answer as the first formula, but is good enough for many calculations.

This simple experiment was the first really scientific method to determine bullet velocity and the book that it was published in revolutionized military science. This method remained in use for quite a while into the mid 1800s before becoming obsolete. However, it is still seen in high-school physics labs, to teach the concepts of momentum and velocity.

Sunday, January 9, 2011

The term "trigger pull force" is defined as the amount of force that is needed to cause the trigger to release in a firearm. If a firearm has a very light trigger pull a.k.a. a hair trigger, then it can be shot very rapidly, as it takes very little force to activate the trigger. However, it also has a greater chance of accidentally discharging, because of the same reason. On the other hand, if a firearm has a very heavy trigger pull, the user will not be able to shoot rapidly and will also not shoot accurately, because the force of pulling the trigger will usually cause the user to shake the firearm a bit more.

So how does one measure trigger pull force. Well, if one is a gadget junkie and has money to spend, then one could acquire a trigger pull gauge like the two examples below:

The first is a mechanical spring gauge, much like an old fashioned spring balance and the second is a digital gauge. To measure the trigger pull force, the tester cocks the weapon (making sure it is unloaded first), simply fastens the hook end to the trigger and pulls the gauge backwards until the trigger releases the firing mechanism. The reading then shows how much force was needed to release the trigger. The illustration below shows how this is done.

Then there is another simple technique as the image below shows. This one is from a Life Magazine issue from 1937, but the same technique is used to this day in many official shooting competitions.

The tester simply adds weights until the trigger releases. Simple and easy to perform.

Before the reader assumes that this is an outdated method, this technique is still used in official NRA shooting competitions to make sure that no competitor is shooting with too light a trigger.

The above image is an NRA official trigger weight system and is available from some sporting goods stores.

Of course, for the casual user who doesn't want to spend $50-$100+ for gizmos like the ones above, there is a much more lower tech way of measuring the trigger pull force, which gives fairly accurate results as well. The homebrew tester simply acquires some heavy wire, such as a wire clothes hanger, cuts it to length and bends it into a S-shaped hook, using a pair of pliers.

The tester first unloads the gun and makes sure it is empty and then cocks the trigger. Then the tester simply hooks the trigger to the large end of the S-hook and then hangs a plastic shopping bag or a tin can from the small end of the S-hook. The tester then adds weights to the plastic shopping bag until the trigger releases. Then the tester employs an ordinary weighing scale (such as the one used in kitchens) and weighs the hook, the plastic bag and its contents. Multiplying this mass with the acceleration due to gravity gives the trigger pull force.

For testers who don't have access to weighing scales, they simply load the plastic shopping bag with known weights, such as grocery items. For instance, 500 gm. bags of beans, 100 gm. boxes of cocoa powder etc. can be loaded into the plastic bag until the trigger pulls. The weight of the S-hook and the plastic shopping bag and the bags that various grocery items come in are considered to be of somewhat negligible compared to the weight of the groceries themselves, so this method can give pretty good approximate results. For example, using 500 gm. bags of beans, it may be possible to determine that the release point of a certain firearm is between 2 kg. and 2.5 kg. (i.e. between 4.4 and 5.5 pounds) because the trigger didn't release when four 500 gm. bags of beans were in the plastic bag, but adding a fifth one did. Then the tester resets the experiment, adds four 500 gm. bags of beans back into the plastic shopping bag and then starts adding 100 gm. cocoa powder boxes until the trigger releases, at let us say 2.3 kg. Now the tester knows that the trigger release point is between 2.2 and 2.3 kg. Then the tester can repeat the experiment using four bags of beans, 2 boxes of cocoa powder and something else that weighs say 20 gms. etc. to get more accurate results and so on.

In this post, we will look into the technique of measuring pressures inside a barrel, when a firearm is discharged. It is important for people to determine pressures of a firearm with various types and brands of ammunition, because some ammunition may produce too much pressure and therefore cause the firearm to explode. A system that enables one to determine the pressure is therefore very useful to determine which ammunition types may be safely used by a firearm.

The maximum pressure is exerted at the breech end in the firing chamber and decreases further down the barrel tube. That's why published numbers usually only list the chamber pressure. It must be noted that there are a couple of different standards in exactly how the pressure is measured. In our first post about proof testing, there were two organizations mentioned, CIP and SAAMI, that publish firearms data. Unfortunately, they have slightly different ideas about how chamber pressures should be measured. We will study these differences a little while later down in this post. Suffice it to say that CIP doesn't care about the shape of the cartridge when deciding which point to take the pressure reading from, whereas SAAMI has different locations to measure the pressure from, based on the shape and diameter of the cartridge. Therefore CIP and SAAMI numbers don't match up for this reason.

The classic method of measuring pressures goes back to the 1800s and early 1900s. It was the method most in use until about the 1960s. It uses crusher gauges to determine pressures.

It consists of a device that allows mounting of a gun barrel. The gun barrel is drilled at various points where pressure measurements are desired. To each of these holes is pushed a tight fitting stopper and the other end of the stopper is held in place by a precisely machined cylindrical piece, which in turn is supported by a steel screw. The precisely machined cylindrical piece is of uniform density and made of copper or lead, depending on the firearm type. For lower pressure weapons such as shotguns or smaller pistols, a lead cylinder is used, whereas copper cylinders are used for higher pressure applications such as rifle or most handgun cartridges. When the cartridge is fired, some of the gas pushes upwards and drives the stoppers out of their holes. This has the effect of squeezing the copper (or lead) cylindrical pieces against the steel screws holding them in position. The amount of deformation of the copper or lead cylinders is measured very precisely and compared with a chart of similar cylinders which were deformed previously under known pressures and the corresponding value is called the Copper Unit of Pressure (CUP) or Lead Unit of Pressure (LUP) value.

While CUP or LUP values are meant to be compared with the crushing power of a known pressure, this is not always the case. For example, the same amount of deformation can occur from a short duration high-pressure pulse as from a longer duration, but lower pressure pulse. Also, these numbers tend to be a bit lower than peak pressures measured using transducers. Therefore, when measurements are made using crusher gauges, the pressure is listed in mega-pascals (MPa - the SI standard unit of pressure) or pounds per square inch (psi - the imperial standard unit of pressure) followed by the letters CUP or LUP to indicate that the measurements were done using crusher gauges.

The crusher gauge method was the only reliable method of measuring chamber pressures until the 1960s, when cheap piezoelectric devices became available. This method is called the Conformal Transducer method or Piezo method. A piezoelectric transducer (a.k.a. sensor) has the property that it generates electricity as it is crushed. The setup is similar to the crusher gauge method, except that instead of a copper cylinder, a quartz crystal transducer is used. Quartz is a material that exhibits piezoelectric properties. Thus, when the cartridge is fired, the transducer transmits electricity, which can be measured and then compared against values generated by similar transducers, when subject to known amounts of pressure. This method has the advantage of measuring pressures at different instants of time, as the bullet leaves the barrel. Measurements by this method generally read about 15-20% higher than those shown by the crusher gauge method. As piezoelectric sensors have become much cheaper now, this is the method of choice for measuring chamber pressures, though crusher gauge measurements are still around as well.

Here's where the differences between the CIP and SAAMI standards show up. CIP uses a transducer made by the Swiss firm Kistler and requires a hole be drilled into the cartridge case and fired by a specially prepared barrel. SAAMI uses a different transducer, called a conformal sensor, mostly made by a US Company PCB Piezotronics. These sensors don't need holes drilled in the case, but they are more expensive as each one needs to be designed based on the diameter of the cartridge.

CIP standards state that the transducer should be positioned 25 mm. from the breech face, when the cartridge is long enough. If the cartridge is too small, then CIP decides to position the transducer at a shorter distance from the breech face, based on the cartridge model. CIP standards do not care what the shape of the cartridge is.

SAAMI, on the other hand, does care what the cartridge is shaped like. For bottle-necked cartridges, the center of the transducer is placed 0.175 inches (4.4 mm.) behind the shoulder of the cartridge for large diameter (0.250 inches, 6.4 mm.) transducers and 0.150 inches (3.8 mm.) behind the shoulder of the cartridge for small diameter transducers. For cylindrical cartridges, the transducer is located behind the base of the seated bullet at a distance of (0.5 * transducer diameter + 0.005 inches)

Since the two standards have different methods and different points from where to take measurements, therefore the CIP and SAAMI pressure numbers are different from each other for the same cartridge type.

Using a transducer is less expensive than using crusher gauges because the same transducer can be reused over and over again, as long as the cartridges used are the same type. So if a tester wants to repeat the test multiple times to get an average pressure reading, he or she only needs one transducer, if using the piezo method. Compare this to the crusher gauge method where each test needs a new copper cylinder and the costs begin to add up.

The third method involves using a strain gauge. This is a thin, flat piece of wire whose electrical resistance changes as it is stretched or strained. The strain gauge is attached on the outside of the barrel near the front of the chamber. When the firearm is discharged, the barrel expands slightly, which stretches the strain gauge and the change in the electrical resistance can be measured and the pressure calculated. This method is fairly accurate, but not as reliable as the other two methods. However, it has the advantage of being the cheapest method of the three and not requiring as much special equipment as the other two methods.

It must be noted that no test can give a truly accurate pressure reading because there is no way to know what the actual pressure should be. Even if the tester uses 100 identical cartridges with equal amounts of propellant and using the same firearm and test setup, the tester can expect up to a 5% variance in pressure values from cartridge to cartridge, when using the crusher gauge method to measure pressure. With the conformal transducer method, the variance is up to 3% from cartridge to cartridge. This is why the conformal transducer method is proclaimed as more accurate than the crusher gauge or the strain gauge method.

Thursday, January 6, 2011

In our last post, we studied all about proof testing and how it is carried out these days. The reader may also find it of interest to learn how it was carried out in the late 1800s and early 1900s as well. In this post, we will study how testing was done in England during this period, as the tests conducted there were generally regarded to be of high-quality.

It was discussed in our previous post that all firearms that were sold in England had to pass the tests of either the London Proof House or Birmingham Proof House. Even though these two proof houses had different proof-marks, the test procedures they used were identical.

The test procedures specified what types of propellant and bullets and their quantities would be used for testing, depending on the type of firearm being tested. For instance, in the early 1900s, the standard propellants specified for the various tests were powders of the following brands: "Tower Proof", Waltham Abbey's "RFG No. 2" with grain sizes between #4 and #5, Curtis's & Harvey's "TS No. 2", "Colonel Hawker's Duck-Gun Powder" and cordite. Bullets were to be of pure lead, except in the case of rifles where nickel plated bullets were to be used. In the case of shotguns, pellets of size #6 were to be used in the test.

Each manufacturer would deliver firearms to be tested, to a proof-house (either London or Birmingham) in an unmarked condition. The first task at hand was to attach each firearm with a unique identifying number. This ensured that the manufacturer of any particular firearm would be unknown to the testers conducting the tests, so that they would have no opportunity of spoiling the test results if they had a previous prejudice against any particular manufacturer.

The next step was to send the firearms to be tested into a gauging room. This is where the bore of the barrel would be determined. In this room, each tester was equipped with a set of 50-60 gauging plugs from the size of a pea to a couple of inches in diameter. Each tester would determine the exact bore of a barrel using these plugs and then pick up a corresponding steel punch and stamp a number on the barrel corresponding to the plug number that best fit the barrel.

After this, the firearms would be transported a short distance to a loading room. This room was divided into three compartments with very strong brick walls in between, so that in case of an accidental explosion, the damage would be confined to a particular compartment. To minimize casualties in case of accident, only necessary personnel were allowed into these rooms. The floors of these rooms were always kept well swept to ensure that there wouldn't be any loose gunpowder lying around. The floors were also always kept damp for extra safety. In the first compartment, a workman would have a set of numbered copper measuring flasks on a rack. The workman would look at the number stamped on the barrel from the gauging room and pick up the corresponding copper measuring flask and fill it with gunpowder. The measuring flasks were pre-calibrated to charge the barrel with extra gunpowder, depending on the bore of the barrel and how much overcharge was specified by the test procedures. After filling a barrel with gunpowder or an overcharged cartridge, the tester would then add a wad to the barrel and pass it through a small window into the next compartment. In the second compartment, a second workman would fill it with bullets specified for the particular barrel type, then ram the charges home with a copper rod and then pass it to the third compartment. In the third compartment, a workman would prepare the barrels for firing (i.e.) add priming powder or a percussion cap depending on the firearm type.

The prepared firearms would now be moved into the firing room. The firing room was a strongly built building lined with sheet iron and had ventilators that could be operated from outside. The door of this room was also made of iron and the room was designed to contain powerful explosions. Depending on the type of firearms, different proof tests would be carried out (a Provisional Proof Test and a Definitive Proof Test). Some firearm types only required one test (the provisional proof test), but most required both tests to be carried out.

As was mentioned in the previous post, a Provisional Proof Test is a test that is carried out in the early stages of the firearm manufacturing process. It is usually conducted for shotgun barrels, though other firearm types may also have this test. The idea behind a provisional proof test is to discover defects in the barrel early on in the build process, so that the manufacturer does not waste time continuing to build a firearm around a weak barrel. The Definitive Proof Test is generally conducted on a fully assembled firearm and tests the strength of barrel and firing action together.

In the case of the provisional test, the barrels to be tested would be lined up on a grooved rack. A thin line of gunpowder would be poured in a groove in the back, that connected all the barrels together. The thin line of gunpowder would be fired by using a hammer striking a percussion cap and the hammer would be operated from the outside of the firing room. On both sides of the barrels were large heaps of sand to collect all the bullets and ensure that there would be no ricochets. The tester would line up the barrels, leave the room, close all the vents and the door and then pull the firing mechanism trigger from the outside. The thin line of gunpowder would ignite and therefore fire each barrel in sequence. After each barrel in the train had fired, they would open the ventilators and allow the smoke to clear. The barrels would be collected from the room and those that had not fired were reprimed and placed back on the rack. The other barrels would be taken to an inspecting room, where they would be washed and inspected for flaws. In the case of "common barrels", they would be allowed to stand for 24 hours before washing, because any flaws in the barrels would become more obvious by the action of the acid residue of the gunpowder eating into them. All barrels that had no visible flaws would be stamped with the appropriate markings to show that a provisional proof test was done.

Provisional Proof Test conducted by Birmingham Proof House.

Taken from W.W. Greener's The Gun and Its Development Edition from 1910

Click on image to enlarge.

In the case of definitive proof tests, the test would be conducted with the barrel and its firing action attached to it. The definitive proof test was carried out individually for each firearm (unlike the mass-testing for the provisional test). Each firearm would be fired by using a thin thread to manipulate its firing mechanism from the outside of the room. The definitive proof test verified the strength of the barrel as well as the firing action. With the definitive proof tests, barrels that failed would either burst or suffer bulges. Bulged barrels would be returned to the manufacturer to readjust and resubmit for proof. It is said that in one case, a particular barrel was tested and bulged eight times, before passing on the ninth attempt! Firing actions that failed the definitive test would either blow up to smithereens or stay open at the area where the action meets the barrel. In the second case, the manufacturer would hammer the action back closed and case-harden it and resubmit for proving. Any firearms that fired the test charge successfully would then be taken to the inspecting room and cleaned and then examined for any flaws in the barrel or action. All firearms passing this test would be stamped with appropriate markings to indicate that a definitive proof test was done.

After the tests were passed, the firearms would then be sent back to the main receiving room, where the attached unique identifying numbers would be used to sort the firearms by manufacturer and then they would be shipped back to the manufacturers' factories. Only then would the manufacturers finish the firearm (i.e.) attach a quality stock, add engraving, stamp the manufacturer logo on it, adjust sights etc.

To give an idea of the scale of testing involved here, the Birmingham Proof House was equipped to conduct roughly half a million proof tests every year, during the 19th century. During the period 1804-1815, Birmingham manufacturers produced 3+ million firearms with an average failure rate of 2 per 1000 tests.

The proof test procedures conducted in England were of such a high standard that, in most other countries, the authorities would allow importers to sell all firearms with English proof markings without requiring any testing from their own proof-houses!

Wednesday, January 5, 2011

The first type of testing we will study is the Proof Test. The idea behind such a test is to verify the strength of the barrel, breech and firing system of a firearm by deliberately firing an over-pressured cartridge. After this, the firearm is examined to make sure it is still intact and if so, the metal (usually the barrel) is stamped with one or more "proof marks" of the testing agency. The proof marks create indented impressions on the metal surface, so they cannot be accidentally removed. Such a test certifies that the firearm is free from manufacturing defects and will not explode under normal usage conditions. In many countries, proof tests are compulsory; and it is not possible to sell a firearm unless it has been proof-tested by an official testing agency approved by the government.

Some manufacturers in the town of St. Etienne in France started conducting proof tests around the 15th century, when firearms manufacturing started in that area. However, France didn't enact a law to make the test mandatory until the 1900s and hence, it was left to each French manufacturer to decide what the test standards should be or even whether to perform a test or not. In other areas, such as London and Birmingham in England and Liege in Belgium, even before testing became compulsory, most manufacturers used to do private tests in their own factories or in a trade testing house.

Compulsory testing laws were passed in most countries mainly due to the backing of the gunmaker guilds of those countries. By enacting such laws, the guilds sought to prevent the manufacture of firearms and stifle competition from non-guild members, even though they claimed that such laws were designed to protect members of the public. The first such compulsory law was passed due to the lobbying efforts of the London Gunmakers Company (a guild composed of firearm manufacturers around London). The initial bylaws passed by the London Gunmakers Company charter of 1637 marked the first introduction of proof tests in England, but didn't specify an official standard of testing. By 1672 though, they managed to get an enhanced law passed, so that agents of the London Gunmakers Company could legally search premises and run proof tests on any firearms made in London or suburbs within 10 miles, or firearms made of imported foreign parts, or firearms brought into London for sale. In order to enforce a standard, the London Gunmakers Company established the London Proof House which was staffed by employees of the various manufacturers comprising the guild. It wasn't coincidence that most barrels failing the proof test requirements were those made by gunmakers who were not members of the London Gunmakers Company guild (to be fair, most of these were often of much lesser quality than London made guns). On May 10th 1672, Maximilian Henry of Bavaria passed a law that made proof testing compulsory in Belgium and established the Liege Proof House to enforce this law. In Birmingham, most reputable manufacturers had their own private proof facilities and many of them also made their facilities available for use by others, but since proof testing was not compulsory in Birmingham, cheaper manufacturers didn't bother to do this test. After a lot of lobbying by the reputable Birmingham manufacturers, the Birmingham Gunmakers Company was finally formed in 1813 by an act of Parliament and authorized to create its own Birmingham Proof House (which still exists to this day in the same historic building). The Birmingham Proof House conducted the exact same tests as the London Proof House, but had different proof marks to indicate that the tests were done in Birmingham rather than London. The firearms manufacturers in Birmingham benefited by this Act because it was more convenient and faster for them to send their firearms locally to be tested, instead of sending them all the way to London. However, the initial Act passed in 1813 proved insufficient, as many less-reputable manufacturers found legal loopholes to evade it, so another Act was passed in 1815 and in 1855, both of which were also ineffective. Finally in 1868, a suitable Bill was passed which remained in force for a while. This Bill was actually a private Act and not a Statute law and specified that the members of the Birmingham Company would elect their own guardians to enforce the proof test standards. It was also enacted that any person making or selling a barrel that was not proved in either the Birmingham Proof House or the London Proof House would be subject to a fine for each violation and any person forging the proof-marks would be subject to a fine as well and defaulting on payments would result in more severe punishments such as imprisonment, confiscation of assets etc. The English proof test procedures were amended in 1888, 1893, 1896, 1904, 1925, 1954, 1978, 1986, 1989 etc. to account for advances in firearms technology. Thus it became impossible to sell firearms in England that were not proved by either of these two proof houses. Oddly enough, there was no similar compulsory law enacted for any of the British Colonies around the world!

Even though Belgium had also made testing compulsory since 1672, the standards of the Belgian tests were far inferior to the tests conducted in England for a long time. In 1892, Germany also made proof testing mandatory and adopted a standard that was essentially the English standard with minor modifications. Since the German proof testing standard was so similar to the English standard, the German authorities automatically approved any firearms with English proof marks with no further testing, but rejected any firearms with Belgian proof marks until they were re-proven in Germany. Since Germany was a major export market for Belgian manufacturers, the Belgians promptly adopted the higher standards by 1893. During this period, there were proof houses in other European countries as well, such as St. Etienne in France, Wiepert and Ferlach in Austria, Budapest in Hungary etc., but as proof testing was not mandatory in these countries, marks from these proof houses were not as well regarded as those of Belgium, Germany or England.

The types of proof tests applied depended on the firearm being tested. Factors such as muzzle loading or breech loading, whether the barrel has rifling or not, bore of the barrel etc. all determine the type and number of proof tests to be run. In the case of multi-chamber firearms, such as revolvers, each chamber would have to be individually proof tested before the firearm was marked. Each proof house had its own marks based on the type of tests applied to the firearm. These proof marks would be stamped on to the barrel of the weapon, usually on the underside so that they would normally not be visible unless one disassembled the weapon for cleaning. The following picture shows some of the proof marks used by different countries:

Click on the image to enlarge.

In general, there are two types of proof test: The first is theprovisional test which is done mainly on shotgun barrels and is done during the early stages of manufacturing, so that the gun-maker does not waste time continuing to build a gun if the barrel tube is defective. The second is the definitive test which is conducted on a firearm that is completely assembled (or close to completion). It tests the strength of the barrel and the firearm action together.

Depending on the types of tests, one could see multiple proof marks on a single weapon, such as the following:

From left to right, the different marks tell us several things about this firearm. First, the left most icon indicates that a Provisional proof test was run on it and this was administered by the Birmingham Proof House (because of the crown with stylized BP lettering under it). The next mark (12/1) tells us that the weapon is of 12 bore. The next two marks indicate that two additional definitive tests were run on it by the Birmingham Proof House, a Proof test (crown with BP) and a View test (crown with BV). The diamond shape with 12 C on it and the word "CHOKE" next to it indicate that this is a 12 bore weapon with choke-bored barrel.

The above image shows another weapon with proof marks left to right indicating: Provisional proof test run by London Gunmakers Proof House (Lion sitting on top of stylized GP), this is a 12 bore weapon (because of 12/1 mark), two more definitive proof tests were run by the London Proof House, a View test (Crown with V) and Proof test (Crown with GP). The diamond icon with 12 LC indicates that this is a 12 bore choke bored weapon and the "R. Choke" mark indicates that the barrel not only has choke-boring, but also has rifling in it.

The meaning of the proof marks for other countries were similarly organized, as the illustration below shows:

Indian Proof Marks

For example, the presence of a nitro-proof marking indicates that this firearm was also proved using newer smokeless nitro-powders.

These days, there are three main standards for proof testing: the C.I.P test and SAAMI test are for commercial firearms and the NATO EPVAT test for military firearms.

The CIP standard was established in 1914 in Liege, Belgium and ratified by law in 14 member countries (most of which are European) and it is illegal to sell civilian firearms in the member countries without having CIP proof marks from an accredited proof house. CIP also independently publishes data about ammunition dimensions, max. pressure generated by different ammunition types, max. pressure that can be tolerated by different firearms, testing procedures, compatibility between firearms and ammunition combinations etc. The current CIP member countries are Austria, Belgium, Chile, Czech Republic, Finland, France, Germany, Hungary, Italy, Russia, Slovakia, Spain, UAE and UK. In a standard CIP test, a firearm is fired twice with overloaded cartridges that produce 25% more pressure (30% more pressure for pistols, revolvers and weapons using rimfire cartridges) than the standard cartridge it would normally be fired with. After firing two overloaded cartridges, the firearm is disassembled and examined for magnetic flux leakage through fluoroscopic lamp in a dark room. If it passes, the CIP proof marks are stamped on to the metal, along with marks that indicate the date and the lab that performed the tests and the accompanying paperwork details are completed as well. Only then is the firearm sent back to the manufacturer or seller, who can now officially sell the firearm. Every civilian firearm that is for sale in a CIP member country is required by law to pass the tests, whether the manufacturer or seller is from a CIP member country or not. CIP also approves all ammunition that is sold by a manufacturer or importer in a CIP member country. The ammunition manufacturers are required to test each production lot in their factory against the CIP pressure specifications, document the test results and stamp each cartridge box with a CIP approved number that allows them to trace any quality-control problems back to a specific factory and lot number.

Similarly, in America, the SAAMI association (Sporting Arms and Ammunition Manufacturers' Institute) was founded by a group of American firearm and ammunition manufacturers in 1926 at the behest of the US Government and is an accredited standards developer for the American National Standards Institute (ANSI). SAAMI performs tests on weapons intended for the civilian market. SAAMI also publishes several technical documents, such as a list of Unsafe Arms and Ammunition Combinations which details cases where a smaller cartridge (e.g. a .44 magnum cartridge made by company X) could fit in a firearm designed to accommodate a larger cartridge (e.g. a .45 caliber pistol made by company Y), but would be unsafe to use because the cartridge produces higher gas pressures than what the firearm is rated for. Due to differences between SAAMI and CIP test procedures, there are some differences in pressure rating values for the same firearm and cartridge models and some combinations may be listed as unsafe in one standard and safe in the other. One more difference is that while the SAAMI association requires its member companies to follow the guidelines and product standards that it sets, it is not a compulsory standard enforced by any branch of the US government (unlike the CIP tests, which are required by law to sell a firearm or ammunition in a country that is a CIP member). All major American ammunition manufacturers are members of SAAMI and most smaller companies also follow its guidelines, except for a few smaller manufacturers. SAAMI also has other committees, such as one that works with CIP to develop common international standards, wildlife conservation, standards for transport and regulation of firearms etc.

The NATO EPVAT test standard is for military grade firearms. This is a much more comprehensive set of procedures than CIP or SAAMI and uses much more sophisticated test instruments.

Proof tests were instrumental in protecting the end-user from weapon failures and compulsory enforcement of these laws helped reduce firearm-related accidents around the world. This is why they are still mandatory in many countries.

With the new year, we will now study another branch of firearms tech. Before we start, I would like to thank all the readers of this blog for their continued support and kind comments and wish you a very happy and productive year ahead.

With that said, we will now deal with the subject of testing. There are several tests that can be done on firearms, which we will study in the following series of posts. Broadly speaking, there are a few different categories of tests that are done with firearms:

Strength and pressure tests: These test the strength of the weapon to resist heavy pressures, test the pressures at the chamber of the weapon, test the pressures generated by different types of propellants, how much force is needed to pull the trigger etc.

Shooting properties tests: These test accuracy of a weapon over various distances, speed of the bullets, depth of penetration of the bullet, behavior of bullets upon hitting the target, force transferred upon impact, how many pellets hit a target per square inch for shotguns etc.

Reliability tests: These test the weapon against various usage conditions, e.g. under cold weather, humid conditions, dirty and muddy conditions, user who doesn't clean his weapon often etc.